This invention relates to machines and sub-assemblies thereof for manufacturing hollow articles from thermoplastic materials by blow molding.
Blow molding is a fabrication method for hollow thermoplastic shapes.
Two general classes of plastic products are made in this manner packaging products and technical parts. Packaging products include such items as bottles, jars, jugs, cans, and the like containers. Technical parts include automotive components such as bumpers, fuel tanks, functional fluid containers, ducting, and the like.
The blow molding process can be of two general types: extrusion blow molding and injection blow molding. In extrusion blow molding, a parison is lowered between mold halves from an extruder. The mold halves then close around the parison, and the parison is then expanded against a mold cavity by introduction of a blowing gas, usually air. In injection molding, a thermoplastic material is first injection molded into a preform parison which is then transferred to a blow mold and expanded in the same manner as in an extrusion blow molding process.
In continuous extrusion, a molten parison is produced from an extruder die without interruption, and a segment thereof is severed and positioned into a mold. The molds can be moved from station to station on rotating vertical wheels, on a rotating horizontal table, or with a reciprocating action. When the parison is extruded, the mold is moved under the extruder die head to receive the parison segment and then is moved to a blowing station.
The positioning of the parison relative to the mold in a rotary system is relatively difficult, thus most of the current blow molding machines utilize the reciprocating mold concept according to which the molds are shuttled back and forth from station to station. A major drawback of the reciprocating mold concept, however, is a limitation on production rate.
In intermittent extrusion, the molds are mounted to a common platen and the parisons are extruded by either a reciprocating screw extruder or by a ram accumulator which holds in readiness a volume of molten plastic material needed to make the next part or parts.
In injection blow molding the parison in first injection molded to a predetermined shape and then transferred to a blow mold to be blown into a finished product.
In all cases, however, the parison has to be transported from station to station to complete the fabrication of a hollow plastic article.
In view of the relatively large commercial demand for various types of plastic articles, it would be desirable to have a blow molding machine of relatively high capacity that can produce high quality articles at a relatively low cost. The present invention satisfies this desire.
The present invention provides a blow molding machine capable of relatively high production rates at relatively low cost.
The foregoing advantages are achieved by a multi-station blow molding machine in which a single parison insertion station is shared by more than one rotary mold array. In particular, the present multi-station blow molding machine is suitable for fabrication of hollow articles from parisons or tubular thermoplastic blanks and includes a base and a pair of rotatable, indexable dials each of which carries a pair of opposed blowing mold clamp assemblies that are indexable to a common parison insertion station but to separate blowing and take-out stations for each indexable dial. A drive is provided for each indexable dial, and the indexable dials can be driven independently or synchronously, as desired, as long as interference between the dials is avoided. The indexable dials are supported on a base for rotation about spaced, substantially parallel vertical axes.
A blowing mandrel assembly mounted to a frame is provided at each blowing station for blow molding hollow thermoplastic articles. A blowing mandrel assembly particularly well suited for use with the present rotary multi-station blow molding machine has a housing that contains an array of reciprocatable blowing mandrels. The number of blowing mandrels provided in any given instance is dependent upon the number of cavities in each mold. A spring-actuated, apertured bushing plate is part of the housing and serves to guide the blowing mandrels from a rest position to a blowing position when a parison-bearing mold is presented at a blowing station.
The housing is defined by the apertured bushing plate, a pair of upstanding guide bars with an end portion thereof affixed to the bushing plate, an apertured mounting plate which slidably receives the guide bars, and an apertured lift plate which is affixed to the guide bars at a mid-portion thereof and serves to lift the bushing plate together with the blowing mandrels as the blowing mandrels are elevated from a blowing position to a rest position. The lift plate is provided with at least one aperture sized to receive a blowing mandrel.
Plural blowing mandrels are slidably mounted to the housing and extend into aligned apertures defined by the bushing plate and by the mounting plate. A biasing coil spring is situated around each guide bar and is positioned between the lift plate and the mounting plate. When the blowing mandrel assembly is in the rest position, the biasing coil spring is in a compressed state. When compression is released, the biasing coil spring exerts a downwardly driving force against the lift plate and urges the lift plate, together with the bushing plate, downwardly toward a mold assembly positioned thereunder. Distal end portions of the blowing mandrels extend through the bushing plate when in the blowing position. A spacer stop, which can be a rigid tubular sleeve or the like, is provided on at least one blowing mandrel that is slidably received in an aperture defined by the lift plate and serves to limit the travel of the lift plate in an upwardly direction when the blowing mandrels are raised to the rest position.
Each blowing mandrel is provided with an actuator that reciprocates the blowing mandrel between a relatively lower blowing position and a relatively higher rest position. The actuator is connected to a proximal end portion of the blowing mandrel through the mounting plate and is affixed to the mounting plate of the housing. The actuator can be a hydraulic cylinder, a pneumatic cylinder, a solenoid device, or the like, as desired.